1. Field of the Invention
This invention relates to optical instruments such as cameras or lenses and, more particularly, to an optical instrument having an electronic circuit such as a microcomputer incorporated therein.
2. Description of the Related Art
Recently, high grade electronic technology has found use in cameras serving as the optical instrument. Such a camera contains a microcomputer and a great number of electronic circuits. Hence, rather than calling it the optical instrument, it would be apposite to call it an "electronic instrument".
In particular, as automatic focusing prevails, the high grade of electronic technology is applied to the control system of the camera. Among the recently developed single lens reflex cameras, there are ones in which not only the camera body but also the interchangeable lens has a microcomputer and an electric motor, as, for example, disclosed in U.S. patent application Ser. Nos. 014,021 filed Feb. 12, 1987, 136,732 filed Dec. 12, 1987, 012,862 filed Feb. 10, 1987, 136,976 filed Dec. 23, 1987, 877,264 filed June 23, 1986, 915,019 filed Oct. 3, 1986, and 016,653 filed Feb. 19, 1987. In the cameras of the character described above (the interchangeable lens contains its own electronic circuits including the microcomputer and its own motors), for example, that of U.S. patent application Ser. No. 136,976, provision for the electrical energy supply to the motors and the microcomputer or the electronic circuits in the interchangeable lens is made by the camera body. The interior of that camera body, therefore, accommodates an electric power source or battery for supplying a current to the motors and a constant voltage device for supplying a current to the electronic circuits. In this camera, the completion of the coupling operation of the interchangeable lens to the camera body immediately starts an electric current being supplied from the constant voltage device in the camera body to the microcomputer in the interchangeable lens, thereupon rendering the microcomputer operative. Meanwhile, the power delivery system for the connection from the power source or battery in the camera body to the various motors in the interchangeable lens is made to operate in such a manner that after the normal coupling of the interchangeable lens to the camera body has been detected and information has normally been communicated between the camera body and the interchangeable lens, an electric current is then permitted to flow through the power delivery system.
In the above-described camera, because it is after the establishment of the normal coupling of the interchangeable lens to the camera body and the start of the normal communication of information between them that an electric power current flows to the power delivery system, there is no possibility of occurrence of wasteful electric current flow to the power delivery system. However, to the microcomputer in the interchangeable lens, regardless of whether or not information is normally being communicated between the interchangeable lens and the camera body, an electric current of relatively large intensity is caused to flow. Even in the substantially unusable state of the camera (for example, the state of abnormal coupling of the interchangeable lens to the camera body, or the state of occurrence of an accident or insufficiency of the insulation or poor connection in the information communication system between the camera body and the interchangeable lens), therefore, a relatively large current continues flowing to the microcomputer in the interchangeable lens. As a result, there is a problem of premature consumption of the battery in the camera body.